Ultraviolet (UV) radiation has been utilized in various applications including biomedical and analytical instrumentation, defense, biotechnology, medicine, air, water, and surface sterilization and decontamination, bio-agent detection and identification, radiation hard UV sources, and UV curing. In many instances, UV radiation is used to manipulate the surfaces of objects, such as in sterilization, but various advanced manipulation of objects and their surfaces are feasible with UV radiation. For example, UV curing technology applies ultraviolet light to resins such as coatings, adhesives, marking ink and photo-resists, etc., to cause photopolymerization. UV technology has also been applied in medical applications, such as skin cancer treatment, sterilization, and increasing vitamin D3 (cholecalciferol). Vitamin D3, for example, is produced through the action of ultraviolet irradiation on its precursor 7-dehydrocholesterol. Vitamin D3 can be made by exposure of the human skin to UV, or by exposing milk directly to UV. Another use for UV radiation is found in food preservation and food modification applications.
Reliable, hygienic storage of sanitary and biological items, such as food, is a major problem. For example, the problem is present throughout the food industry, e.g., manufacturers, retailers, restaurants, and in every household, and is especially significant for food service establishments, in which related issues of food quality control also are significant. In addition to food storage and quality control in fixed locations (e.g., a refrigerator) where access to electricity is readily available, proper food storage and quality control also is important in situations for which access to unlimited electricity and/or a stationary storage device, such as a refrigerator, is not available, such as picnics, camping, mobile food kiosks, hospitality or battlefield meal locations, search and rescue, etc. In addition to food, other stored items also require hygienic storage. For example, medical and chemical equipment, construction wood, etc., also require storage in a biologically safe environment. Since ambient temperature significantly affects bacterial activity, effective control of the ambient temperature is an important tool in ensuring reliable, hygienic storage of various items.
Fresh food products can be processed using ultraviolet light as a germicidal medium to reduce the food-born microbial load. Water has been treated with ultraviolet light to provide safe drinking water for quite some time. Fruit and vegetable products capable of being pumped through a system generally are very suitable for processing by ultraviolet light to reduce the microbial load. Today, most of these products are pasteurized to obtain microbiologically safe and nutritious products. However, pasteurization can change the taste and flavor of such products because of the temperature and processing time. Juices from different sources can be treated by exposure to ultraviolet light at different doses. On the other hand, variables such as exposure time, type of fruit product, juice color and juice composition, among other variables, need to be studied to obtain fruit products with reduced microbial load, increased shelf life and adequate sensory and nutritional characteristics. Reduction of microbial load through ultraviolet light application as a disinfection medium for food products other than liquids also is being studied. Moreover, ultraviolet technology could be a source for pasteurization of liquids, or disinfection of solid foods as an alternative technology, instead of thermal treatment or application of antimicrobial compounds.
In general, ultraviolet (UV) light is classified into three wavelength ranges: UV-C, from about 200 nanometers (nm) to about 280 nm; UV-B, from about 280 nm to about 315 nm; and UV-A, from about 315 nm to about 400 nm. Generally, ultraviolet light, and in particular, UV-C light is “germicidal,” i.e., it deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease. This effectively results in sterilization of the microorganisms. Specifically, UV-C light causes damage to the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in the DNA. The formation of these bonds prevents the DNA from being “unzipped” for replication, and the organism is neither able to produce molecules essential for life process, nor is it able to reproduce. In fact, when an organism is unable to produce these essential molecules or is unable to replicate, it dies. UV light with a wavelength of approximately between about 250 to about 280 nm provides the highest germicidal effectiveness. While susceptibility to UV light varies, exposure to UV energy for about 20 to about 34 milliwatt-seconds/cm2 is adequate to deactivate approximately 99 percent of the pathogens.
Various approaches have sought to use ultraviolet light to disinfect a compartment, such as compartments found in refrigerators. For example, one approach proposes a plurality of small, low current UV lights which utilize the standard circuitry of the refrigerator to power the UV light source. Another approach uses a UV lamp installed in a top portion of the refrigerator and reflective lining throughout the interior to reflect the UV radiation throughout the compartment. Another approach provides a UV system with a single UV source attached to an internal sidewall of a refrigerator to radiate light to the entire compartment, or in the alternative, provide UV exposure to a limited compartment. Still another approach proposes an air cleaner for an internal compartment of a refrigerator, which utilizes a UV filter to reduce pathogens in the re-circulated air. Still another approach provides a refrigerator with UV light irradiation components to eradicate low-level light from the storage containers contained therein to promote freshness of foodstuffs.